You can get the same lighting pattern with an umbrella, that's the easy part. But there are differences.
For example, an umbrella tends to spill light all over the place, so if you are in a small space with reflective walls, your background may get a lot more light with an umbrella, than it would with a softbox. So it might be harder to pull off a dark field shot like this.
Another way that light modifiers will differ, is how the light falls off and transitions into shadow. This will change even from one softbox to another or one umbrella to another. It will change depending on how close the umbrella is to the light etc.
If you Google 'light modifier comparison' you should come up with several sites that show you examples of what the photos will look like with different modifiers. Sometimes it's a subtle difference, sometimes not.
Here is one I found....
MODIFIERS